1. Field of the Invention
The present invention relates to an engine which has two systems of fuel injection nozzles, one of which includes fuel injection nozzles for direct injections in cylinders and another of which includes fuel injection nozzles for port injections. The engine controls fuel injection by selectively using one of the systems when the engine is started.
2. Description of the Related Art
There is an internal combustion engine provided with a fuel injection valve for cylinder injections and a fuel injection valve for intake port injections. Improvement of fuel efficiency is attempted by selectively using one of the two fuel valves in accordance with the driving state. Since the engine temperature is low, what is called “cold state”, when the internal combustion engine is started, a combustion state is not stabilized in order that evaporation of fuel does not proceed. It is expected that the vaporization of fuel is facilitated by making the pressure of fuel injected from the fuel injection valve for the cylinder injection in the cylinder high, but there is no residual pressure in many cases when the internal combustion engine is cold state, and it takes a while to sufficiently increase the injection pressure.
An internal combustion engine described in Patent Document 1 includes a main injector for injecting and supplying fuel directly into a cylinder, and a sub-injector for injecting and supplying fuel into an intake passage. A fuel injection control unit of this internal combustion engine injects fuel in an intake stroke from at least the sub-injector when the fuel injection pressure measured by a pressure sensor is lower than a predetermined pressure and when temperature of engine cooling water measured by a temperature sensor is lower than predetermined temperature. It is described that even if the pressure of injected fuel is low and the diameter of fuel particles is large, the fuel is vaporized before it is supplied to the cylinder, and is mixed with air.
An internal combustion engine described in Patent Document 2 includes an intra-cylinder injector for injecting fuel into a cylinder and an intake passage injector for injecting fuel into an intake passage. When the internal combustion engine is started, a control unit of the internal combustion engine injects fuel only from the intra-cylinder injector when the internal combustion engine is warm, and the control unit injects fuel only from the intake passage injector when the internal combustion engine is cold. Fuel is injected by the intra-cylinder injector during a compression stroke, and fuel is injected by the intake passage injector during an intake stroke. It is described that even if the internal combustion engine is cold, vaporization of fuel is facilitated by injecting fuel into the intake passage as in Patent Document 1.
An internal combustion engine described in Patent Document 3 includes a port injection valve arranged in an intake passage of each of cylinders, and intra-cylinder injection valves arranged in at least two of the cylinders. The intra-cylinder injection valve is arranged in each of the cylinders which are arranged such that a stroke is brought into a compression stroke or a power stroke when an arbitrary one cylinder and this cylinder are brought into a stroke other than the compression stroke or other than the power stroke. When it is required to start the internal combustion engine, a control unit of the engine injects fuel into cylinders which are in the intake stroke and the exhaust stroke by the port injection valve, and injects fuel into cylinders which are in the compression stroke or the power stroke by the intra-cylinder injection valve. It is described that since the engine is configured as described above, even if the crankshaft stops at any angle, initial combustion is swiftly obtained from a cylinder into which fuel is injected by the intra-cylinder injection valve at a first cycle of start of the engine, and the engine is swiftly started.
It is also described in Patent Document 3 that all of cylinders in an in-line four-cylinder internal combustion engine have intra-cylinder injection valves and port injection valves. According to this internal combustion engine, at the point of start requirement to start the engine, two of the cylinders are surely in the compression stroke and the power stroke irrespective of the angle of rotation of the crankshaft. According to this, stronger initial combustion is obtained. An example in which the same technique is applied to a V-six engine is also described. It is described that the intra-cylinder injection valves are arranged in any one of the cylinders and a cylinder which is deviated in phase from the former cylinder through 360° in the crank angle and according to this, initial combustion is reliably obtained in a first cycle.